The invention relates to a method of dust-free and vacuum-tight interconnecting ceramic aluminum-oxide components in a protective gas atmosphere, using a solder material which connects the components by heating.
In a first known method of connecting ceramic components the ceramic is metal-plated before the soldering operation to obtain an appropriate wetting ratio of the solder during soldering. For that purpose in a known method, commonly referred to as a Mo-Mn method, molybdenum particles (Mo) and a residual quantity of manganese (Mn) and silicon dioxide (SiO.sub.2) are, for example, fused into the ceramic in a moist, protective gas atmosphere (H.sub.2 /N.sub.2). The resultant manganese oxides combine with the aluminum oxide ceramic (Al.sub.2 O.sub.3) while forming a mixed oxide. The vitrifying silicon dioxide improves the embedding and the adhesion of the molybdenum particles. The molybdenum particles, which optionally are additionally provided with a dull nickel layer and project from this cover coat, applied bymetal plating, enable bonding to the metal solder. In a similar method, disclosed in the German Patent DE No. 700,840, a metal is sintered onto the ceramic before soldering. The soldering operation is effected subsequent thereto in a weakly reducing atmosphere.
In a further known method of soldering ceramic aluminum-oxide components, metal-plating of the ceramic surface to be soldered is not required. In this method what is commonly referred to as an activated solder is used during the soldering operation. In addition to the basic solder, activated soldering materials additionally include alloying, highly reactive metals, for example titanium (Ti) or zirconium (Zr). These alloying metals are referred to as active components and have a particularly high affinity to oxygen. These properties are used to partly draw the oxygen from the aluminum oxide ceramic, to produce oxides of these metals. The oxide of the titanium or of the zirconium thus obtained can be dissolved in the ceramic oxides while forming a mixed oxide. These oxides diffuse into the surface of the ceramic, taking the basic soldering material along, and thus produce a proper connection. The connection or wetting, respectively, occur however only in those places which are in direct contact with the solder. This implies that no flow into possibly existing capillary joints occurs.
These known methods of soldering ceramic aluminum-oxide components have however some disadvantages. In the first method, in which the ceramic is metal-plated to ensure an a adequate adhesion and wetting of the soldering material to the ceramic, the metal-plating operation requires up to six process steps which render the method very complicated and consequently not very economical. The second method requires activated soldering materials, only very few of which are commercially available. In addition, these activated soldering materials are very expensive because of the admixture of metals which are highly reactive with oxygen. Moreover, this solder is not capable of completely filling the joint between the parts to be connected, as the active component only acts in that region where the soldering material was deposited before heating.
Swiss Patent CH No. 328,016 discloses a method of interconnecting ceramic objects or for joining two metal objects, in which a special paste is used consisting of a mixture of silver oxide and copper oxide. The paste is applied to the ceramic materials before soldering. The ratio of mix of the two oxides in the paste determines during the ultimate soldering operation the quality of the wetting of the ceramic and the adhesive power of the soldered joint. The specific disadvantage of this method is that it requires the production of a special paste. In producing this paste it is necessary for the ratio of mix of the two oxides in the paste to be adjusted accurately, because of which the production offers some problems.